Hydraulics Prof. B.S. Thandaveswara

Indian Institute of Technology Madras

28.2 Classification of Jumps

As mentioned earlier, the supercritical flow Froude number influences the

characteristics of the hydraulic jump. Bradley and Peterka , after extensive experimental

investigations, have classified the hydraulic jump into five categories as shown in

Figure 28.4.

The hydraulic jump is the phenomenon that occurs where there is an abrupt transition

from supercritical (inertia dominated) flow to sub critical (gravity dominated) flow. The

most important factor that affects the hydraulic jump is the initial Froude number 1F .

11

VFgD

=

in which 1V is the longitudinal average velocity at the initial section, g is the acceleration

due to gravity and D is the hydraulic mean depth (ratio of area of flow at free surface

width).

As mentioned above, it occurs in a straight prismatic horizontal channel of rectangular

shape in which boundary friction is negligible (NHJ).

The hydraulic jump can be classified based on initial Froude number as

Undular ( )1 1 1 7F .= , weak ( )1 1 7 2 5F . .= , oscillating jet ( )1 2 5 4 5F . .= , steady ( )1 4 5 9 0F . .= and strong ( )1 9 0F .> .

Hydraulics Prof. B.S. Thandaveswara

Indian Institute of Technology Madras

Undular jump 1.0 < F1 < 1.7

Weak jump 1.7 < F1 < 2.5

Oscillating jump 2.8 < F1 < 4.8

Steady jump 4.5 < F1 < 9.0

Strong jump F1 > 9.0Fig. 28.4 - Classification of the Jump

Hydraulics Prof. B.S. Thandaveswara

Indian Institute of Technology Madras

Type of Jump Froude Number Remarks

Critical flow 1F 1= Wavy surface , celerity

c gy= Undular jump 11 < F 1 7.< Undulations on the surface Weak jump 11.7 < F 2 5.< Small rollers, No baffles.

Oscillating Jump

12.5 < F 4 5.<

No periodicity. Rip rap may get damaged

Canal drops, difficult to handle.

Baffle blocks or appurtenances are of little value. Wave suppressors may be designed.

Steady jump 14 5 < F 9 0. .< Position, is sensitive to

variation of Tail Water,

Efficiency is 45 to 70 %. Strong Jump 1F 9 0.> Efficiency is 85 %

The jumps can also occur on horizontal bed or sloping bed. The jump can take place in

radially diverging, radially converging, rectangular, sudden convergence or expansions

in plan. The jump can occur in different shape of the cross section of the channel such

as rectangular, trapezoidal, parabolic, circular channels. The jump can occur in the

conduit either at the free surface or fully flowing downstream condition. The annular

jump is yet another type. The jump can be either free (unsubmerged) or submerged

condition such as in the downstream of sluice gates. The jump can be a forced one with

the appurtenances (such as baffles, sills, chute blocks) or free (i.e. either without any

appurtenances). Jump could be either stationary or moving (hydraulic bore).

The jump can be in stratified flows such as warm and cold water (flowing over each

other), air and water (classical jump) or in case of gas to gas (internal jump).

The Important macroscopic parameters are initial depth 1y , sequent depth 2y , Initial

mean velocity 1V , mean velocity at the end of the jump (exit velocity) 2V , length of jump

( )jL and the roller ( )rjL .

Hydraulics Prof. B.S. Thandaveswara

Indian Institute of Technology Madras

Classifications of Jumps

I. Based on Froude Number

Undular, weak, oscillating, steady and strong (See the figure - 2 above)

II. Based on Bed Slope

Horizontal

,

Sloping

III. plan shape of boundary

Rectangular

Radial Diverging Channel

Radial Converging Channel

Sudden Expansion

Hydraulics Prof. B.S. Thandaveswara

Indian Institute of Technology Madras

IV. Shape

y1

y2

Rectangular

T

b

m1

m1

Trapezoidal

y1

y2

T

m1

m1

y1

y2

Triangular

T

do

Circular free surface flowy

1

doy

1

Circular free surface to Pressure flow

Hydraulics Prof. B.S. Thandaveswara

Indian Institute of Technology Madras

V. Fluid Status

Water

liquidGas

Air

Classical Hydraulic jump

Gas to Gas Internal jump

liquid (warm)1

2 liquid (Cold)Liquid to Liquid ( 2 > 1 )

VI. Submergence

Sluice Gate

1

Hydraulicjump

2

3

Rapidly varied flow with Hydraulic jump (1 and 3 subcritical flows,2 Super critical flow)

Free Jump (Not Submerged)

Sluice Gate

1

2

3

Rapidly varied flow with Hydraulic jump (1 and 3 subcritical flows,2 Super critical flow)

Submerged Jump

Tail water depth is greaterthan the sequent depth

VII. Motion

Stationary Jump

Moving Jump

Example: Hydraulic Bore

VIII. Appurtenances

unforced or Free

Hydraulics Prof. B.S. Thandaveswara

Indian Institute of Technology Madras

Free Jump (Unforced)(without Appurtenances)

Forced

Chute block Baffles or Piers or floor blocks End SillForced Jump (with Appurtenances)

Hydraulics Prof. B.S. Thandaveswara

Indian Institute of Technology Madras

Jump in gradual expanison - looking downstream

Hydraulics Prof. B.S. Thandaveswara

Indian Institute of Technology Madras